Methods of decomposing sample have used beakers and watch glasses to decompose samples for about hundred years. Although using beakers has the advantage of allowing simple sample decomposition, a large amount of volatile elements, such as mercury and arsenic, are lost through the open upper portion and a large amount of reagents are used by evaporation of the reagents due to heating. Further, the generated harmful gases damage the main body of the heater and reduce the life of the fume hood.
Further, a method has been proposed, which places a cooling tube having a size of 25 cm or more on a round bottom flask of 250 ml, installs an collection tube, and then decomposes a sample with an acid. The cooling tube is a water-cooling type and requires a separate electric chiller. Since the method has a large equipment length, it is difficult to use the equipment on a common hood and to clean the equipment after decomposition. Further, since it can treat at most five samples at one time, it is not suitable to decompose many samples. Further, in terms of technology of the method, the gas evaporating in the reaction vessel condenses and falls down too much, it cannot used for when a large amount of acid requires to evaporate. Therefore, the collection tube has difficulty in achieve the original function due to the water-cooling type cooling tube. That is, most gas evaporating in the reaction vessel falls down in the reaction vessel by the cooling tube, failing to rise to the collection tube, such that there is little relationship between the reaction vessel and the collection tube.
Recently, a method of decomposing a sample using a microwave is commonly used. However, since the microwave performs pressure decomposition, the amount of sample injection is limited. In general, it cannot decompose an inorganic substance of above 0.5 g. Further, the pretreatment of a sample is complicated in the method.    [Document 1] See drawings of pretreatment of zinc and nickel of Korea Soil Test    [Document 2] US EPA Method 3015, 3051, 3052